JP5419452B2 - Light source and method for generating light of variable color and / or brightness - Google Patents

Abstract

The present invention relates to a light source, which produces light leaving the light source with modifiable color and luminosity, with at least one light emitting diode for emitting primary radiation, comprising a layer connected with said diode, wherein said layer includes at least one luminescent material for converting the primary radiation into a secondary radiation.

Description

  The invention relates to a light source comprising at least one light emitting diode emitting primary radiation, the light source comprising a layer connected to the diode, wherein the layer converts the primary radiation into secondary radiation. It relates to a light source containing materials.

  Light emitting diodes (LEDs) such as phosphor converted LEDs are known to generate light with a high color rendering index. However, the color temperature of light is fixed for each individual phosphor conversion LED in a wide color temperature range.

  A significant disadvantage is that by increasing the excitation density to the phosphor, the phosphor begins to saturate due to ground state depletion or thermal quenching of the emission. During the saturation process as described above, the layer with the luminescent material increasingly transmits primary radiation. Thus, the color of the light leaving the light source (mixing of the primary and secondary radiation) is changed. One disadvantage of such known light sources is that the color of the light exiting the light source changes when the brightness of the light changes. Another problem is that the temperature of each diode increases due to the increase in power loss as described above.

  The object of the present invention is to eliminate the above disadvantages. In particular, the object of the present invention is a light source that is simple and can be easily tuned to generate light, the color and / or brightness of the light without substantially increasing the temperature of the light emitting diode. It is to provide a light source that can be easily changed.

  This object is achieved by a light source as taught by the appended claim 1 of the present invention. Thus, switching in which the diode is driven by a pulsed current to provide light containing primary and / or secondary radiation in such a way that each of the brightness and color of the light can be varied independently. A light source including the apparatus is provided. This means that the brightness of the light can be changed without a change in the color of the light and / or the color of the light can be changed without a change in the brightness of the light. Means.

Preferably, the pulse shaped current is pulse width modulated, so that in possible embodiments the primary radiation may be visible light or invisible light. According to a preferred embodiment of the present invention, the primary radiation is near ultraviolet light (first peak wavelength is in the range from 250 nm to 380 nm) or blue light (first peak wavelength is from 380 nm). In the range of 480 nm). One essential idea of the invention is that when driving the diode with a pulse-shaped current, the overall light output can be controlled by the number of pulses, whereas the saturation of the luminescent material. Is based on the fact that it can be adjusted by the energy density per pulse (units J / cm ² / s). With this device of the invention, the diode emits primary radiation radiating into the layer. Advantageously, the fluorescent material comprises a phosphor excited by photons from the primary radiation.

  Depending on the excitation density of the pulse-shaped current (especially of the primary radiation), the luminescent material begins to saturate due to a lack of ground state. During this saturation process, the fraction of the primary radiation that is converted to the secondary radiation by the phosphor is reduced compared to the situation where no saturation occurs. Depending on the phosphor, the secondary radiation can be converted into various colors. Of course, the present invention can be driven in such a way that a change in color is accompanied by a change in luminance and a change in luminance is accompanied by a change in color.

  Advantageously, the color and brightness of the light can be adjusted independently of each other by using pulse width modulation (PWM). The degree of saturation is determined by the energy density within the pulse, and the brightness is adjusted by the frequency of the pulse. Thus, the tunability of the color and brightness is accompanied by an unacceptable increase in the power loss of the LED, which can result in thermal quenching of the phosphor emission and thermal degradation of the LED encapsulation. Can be obtained without. Finally, by using the present invention in combination with a sensor, the color point of the LED light can be kept constant for a long time.

  Preferably, the layer is a ceramic phosphor layer. Depending on the level of saturation, the primary radiation emitted by the diode is more or less transmitted through the layer. The light exiting the light source includes the primary radiation and / or secondary radiation. Thus, the color of the light is generated by a mixture of the primary and / or secondary radiation colors. In a preferred embodiment of the invention, the primary radiation is blue light. For example, when CaS: Eu is used as the phosphor element in the layer, the primary radiation is converted by the phosphor into secondary radiation having a red color. Depending on the degree of saturation of the phosphor, some blue radiation is transmitted through the layer, so that a certain amount of red radiation is generated by the phosphor. The resulting light is a mixture of the red radiation and the blue radiation. When saturated, the transparency of the layer for the blue light is increased. According to the invention, all colors located on the line in the xy chromaticity diagram between the primary color (blue) generated by the LED and the red emission color generated by CaS: Ce are said light source Can be generated for such light exiting. One of the main advantages is that one current light source with one diode can produce the resulting light with a variety of variable colors.

Further, the layer preferably has one or more of the following phosphors.
(Red light)
CaS: Eu, SrS: Eu, (Ca, Sr) S: Eu, (Y, Gd) ₂ O ₂ S: Eu, Y (VO ₄ ): Eu, (Sr, Ba, Ca) ₂ Si ₅ N ₈ : Eu
(Green / yellow light)
_{Y 3 Al 5 O 12: Ce} , (Y, Gd) 3 Al 5 O 12: Ce, (Ba, Sr, Ca) 2 SiO 4: Eu, CaS: Ce, ZnS: Cu, La (PO 4) :( _{Ce, Tb), (Ce,} Tb) Al 12 O 19, (Ce, Gd, Tb) MgB 5 O 10, BaMgAl 10 O 17: Eu, Mn, ZnS: Au
(Blue light)
CaS: Cu, SrS: Ag, ZnS: Ag, BaMgAl ₁₀ O ₁₇ : Eu or (Ca, Sr, Ba) ₅ (PO ₄ ) ₃ Cl: Sb, (Ca, Sr, Ba) ₅ (PO ₄ ) ₃ Cl : Eu
(White light)
(Ca, Sr, Ba) ₅ (PO ₄ ) ₃ (F, Cl): Sb, Mn, (Ca, Sr, Ba) ₅ (PO ₄ ) ₃ (F, Cl): Eu, Mn

  For example, the color of the light can be generated by mixing the primary radiation and the secondary radiation. White light can be achieved by combining the colors blue and yellow and blue as described above. Another possibility is to combine the green and red colors as described above.

  By using white light emitting phosphors as described above, differences in the saturation behavior of sensitizing and activator ions can be used to tune the color and brightness. .

  Preferably, in the phosphor mixture, the phosphors described above have different saturation behaviors. This means that by exciting the layer with a pulsed current having a certain density, some of the phosphors can be in the unsaturated mode, so that other embedded phosphors It means already in saturation mode. Thus, the light source can generate all possible colors by driving the diode with some pulsed current generated by a switching device connected to the light source.

According to another preferred embodiment of the invention, the layer has a density d of the phosphor material that is 1.5 g / cm ³ ≦ d ≦ 10 g / cm ³ .

  According to the present invention, the light source can have a layer having a thickness n where 1 μm ≦ n ≦ 1 mm, whereby the layer can be formed by fitting, adhesive bonding and / or forming a frictional connection to the diode. Can be connected to. In a further preferred embodiment, the thickness n can be in the range of 10 μm ≦ n ≦ 500 μm. Indeed, in an alternative embodiment, the thickness n of the layer may be greater than 1 mm, for example 1 cm. In this case, the light emitting layer as described above may have the form of a ceramic layer. Alternatively, the luminescent material may be embedded in glass.

Further, it is preferable that the layer includes phosphor particles, and the layer has at least one granular layer. Preferably, the layer has x number of granular layers of a plurality of 1 ≦ x ≦ 10. In a more preferred embodiment, the layer includes x number of granular layers is 2 ≦ x ≦ 5. While driving the diode with a pulsed current, this granular layer produces some scattering of the primary and / or secondary radiation, which is important for the mixing of the light leaving the light source. The strong scattering of the light must be considered to reduce or even prevent the transmission of the LED pump light through the phosphor layer. For this reason, a layer having a thickness of 2 to 5 granular layers is preferred.

  The preferred invention as described above is a light source having at least one light emitting diode that emits primary radiation, the light source having a layer connected to the diode, and a method for generating light having different colors. The layer comprises at least one luminescent material that converts the primary radiation into secondary radiation, and a pulsed current having a pulse width (pulse period) and a distance between the pulses (switching off period). The light-emitting material having an attenuation period in such a way that the brightness and color of the light comprising the primary radiation and / or the secondary radiation can be varied independently of each other. , Excited by the primary radiation, whereby the pulse width is approximately equal to the decay period. The pulse width and the pulse height are used to adjust the saturation of one or more of the luminescent materials. Preferably, the switching off period is longer than the decay period of the luminescent material. In a preferred embodiment of the invention, the switching off period is at least twice as large as the decay period, and in a more preferred embodiment, the switching off period is at least 3 to 5 times greater than the decay period.

  One advantage of the present invention is that the brightness of the light leaving the light source can be changed by changing the distance between pulses, so that the color of the light is substantially constant. During the driving of the diode, the switching off period can be reduced, thereby improving the brightness of the resulting light, while the color of the resulting light is not substantially changed. Advantageously, the LED is excited by a fixed pulse width, whereby a change in the energy of the pulse changes the degree of saturation. By increasing the energy of the pulse, the saturation behavior can be achieved. Therefore, the color of the light changes. The result of driving the LED with a long off-period is that the phosphor activator reaches the ground state before the next pulse is applied. Therefore, the brightness can be decreased without changing the color by further increasing the off period. By appropriate adjustment of the pulse height and PWM, the color can be changed without the luminance change. Furthermore, current methods of generating light reduce the effects induced by slight wavelength changes in the emission of the LED when two or more additional colors are generated by the emission conversion layer. In this case, a sensor may be required. Furthermore, the present invention provides an opportunity to correct the effects due to phosphor degradation.

  The light sources and methods described above are various systems among automotive systems, home lighting systems, backlight systems for displays, ambient lighting systems, camera flashes (with adjustable colors) or store lighting systems. Can be used. The components described above, the components recited in the appended claims, and the components to be used by the present invention in the described embodiments are related to the selection of size, shape or material as a technical concept. It is not subject to any special exceptions, so that the selection criteria known in the appropriate field can be applied without limitation.

  Further details, features and advantages of the object of the invention are shown in the appended dependent claims and in the respective figures which are one preferred embodiment of a fashion-show of the exemplary mode of the light source according to the invention. It is disclosed in the following description.

  FIG. 1 shows a light source 1 having one light-emitting diode 2 connected to a switching device 7. On top of the diode 2, a layer 4 having a light emitting layer 5 is located. When the diode 2 is driven by a pulse-shaped current, the diode 2 emits visible light 3 emitted in the direction toward the layer 4. In this embodiment, the visible light 3 (primary radiation) is blue light, and the first peak wavelength is 455 nm. The white diode 2 emits primary blue radiation 3 and the luminescent material 5 embedded in the layer 4 is excited by photons of the blue radiation 3, whereby the blue light 3 is converted into secondary radiation 6. . In the embodiment shown in FIGS. 1 and 2, the luminescent material 5 may comprise a phosphor that emits yellow light during the conversion. In FIGS. 1 and 2 described above, CaS: Eu is used as the phosphor material.

  When the excitation density of pulse width modulation (PMW) is increased, the phosphor 5 begins to saturate due to the lack of ground state. The result obtained is that the phosphor layer 4 further transmits blue pump light. In the unsaturated mode as described above, as shown in FIG. 1, the light source 1 produces light that has a substantially amber color. When the phosphor 5 is saturated, much blue radiation 3 is transmitted by the layer 4. This means that more blue light 3 exits the light source 1 due to the increased transparency of the layer 4 to the blue light 3 when saturated as described above.

  The resulting light includes primary radiation 3 and secondary radiation 6. By changing the excitation density for the phosphor 5, the degree of saturation of the phosphor 5 can be adjusted. Depending on the excitation density, a color of the resulting light that is a mixture of the colors of the primary radiation 3 and the secondary radiation 6 can be generated.

  According to FIGS. 1 and 2, the resulting light of the light source 1 can include all colors between blue and yellow.

The phosphor 5 is embedded in an organic material (which can be, for example, an acrylic or silicon material). The phosphor 5 described above is a single grain 5, whereby the density of the phosphor material 5 in the layer 4 is about 5 g / cm ³ . The thickness of layer 4 is about 10 μm. As shown in FIGS. 1 and 2, the layer 4 is composed of four granular layers 8. The more the layer 4 contains more granular layers 8, the more the resulting light is scattered by the luminescent material 5. This means that when increasing the number of granular layers 8, the resulting light produced by the light source 1 is less. This coherence can also be important with respect to the generation of light from other light sources not mentioned above.

  Surprisingly, when the diode 2 is driven by a pulse-shaped current 9 including the pulse width 10 (pulse period) and the distance between the pulses 11 (switching off period), the primary radiation 3 and / or the secondary radiation 6 is used. The brightness of the contained light and the light can vary independently of each other, so that the pulse width 10 is substantially equal to the decay period. FIG. 3 shows two schematic diagrams of the pulsed current 9 driving the diode 2. Advantageously, when the switching off period 11 is set to a period that is at least three times as large as the decay period, the brightness of the light can be changed without changing the color of the resulting light. In the illustrated embodiment as described above, the switching off period 11 is five times greater than the decay period. As shown in FIG. 3, by shortening the switching off period 11 ′, the brightness of the resulting light is increased, so that the color of the resulting light is substantially constant. Certainly, the distance between the pulses 11 may be smaller than the attenuation period, and in particular may be equal between the attenuation regions.

の関係を示す。 In the above embodiment, saturation due to the lack of ground state is the number of excited photons I, the number of luminescent ions in the excited volume (N) and the phosphor (especially included in phosphor 5). The decay period τ of the active agent emission is

The relationship is shown.

This formula for continuous and quasi-continuous excitation is obtained when the duration of such an excitation pulse is significantly longer than the emission decay period. The saturation effect can also be observed when the duration of the excitation pulse is shorter than the emission decay period. Assuming an emission area of 1 mm ² , phosphor layer thickness of 10 μm, packing density of 50%, phosphor material density of 5 g / cm ³ , molar mass of 100 amu, activator density of 1% and decay period of 1 μs, saturation is about Expected for values I exceeding 10 ²¹ / cm ² . This corresponds to an excitation energy of about 50 W / mm ² . Thus, fast decaying phosphors (decay periods << 1 μs) do not show saturation as a result of ground state depletion when typical concentrations of activator are used. Despite the use of these phosphors, the concentration of activator must be reduced. This includes smaller optical absorption, which can be improved again by using larger phosphor particles. Alternatively, a luminescent material embedded in a ceramic phosphor layer or glass can be used.

In other embodiments not described above, phosphors 5 having activators that exhibit forbidden transitions can also be used if such emission can be made more sensitive. For example, assuming a 1 ms emission decay period, a sensitized emission saturation is already expected at an energy density of about 0.05 W / mm ² . In order to prevent a strong loss of energy efficiency, the release of the higher sensitivity can also be used (energy transfer to the activator excites many of the activator ions. The intensity of the emission of the higher sensitivity increases).

  Alternatively, the layer 4 of phosphor ceramic can have various phosphors 5 that emit secondary radiation 6 during the conversion. For example, the radiation 6 can include green or blue. Preferably, by using phosphors 5 having different saturation behavior, the resulting light of many different colors can be generated. When the excitation density is increased by PMW, the resulting light color changes accordingly.

Certainly, the diode 2 of the above-described embodiment can emit ultraviolet light having a first peak wavelength in the range of 250 to 380 nm. Preferably, CaS: Cu, SrS: Ag, ZnS: Ag, BaMgAl ₁₀ O ₁₇ : Eu or (Ca, Sr, Ba) ₅ (PO ₄ ) ₃ Cl: Sb, (Ca, Sr, Ba) ₅ (PO _{4 3} Cl: Eu is used as phosphor 5 in layer 4. These phosphors 5 are excited by ultraviolet light emitted by the diode 2 and convert the ultraviolet light into blue light. Advantageously, said layer 4 additionally comprises a phosphor 5 which converts the primary radiation 3 into secondary radiation 6 (for example having various colors such as yellow, green or white).

  The present invention also refers to a light source system having an array of one light source as described above.

1 is a schematic diagram of a light source including a diode and a layer having a luminescent material in an unsaturated mode. FIG. Fig. 2 shows the light source according to Fig. 1 wherein the luminescent material is in saturation mode. Fig. 2 shows a schematic diagram of a pulse-shaped current driving the diode according to Fig. 1;

Explanation of symbols

1 Light source 2 Light emitting diode, LED
3 Primary radiation 4 Layer 5 Luminescent material, particles 6 Secondary radiation 7 Switching device 8 Granular layer 9 Pulse shaped current 10 Pulse width, pulse period 11 Switching off period, distance between pulses

Claims (13)

In a light source that generates light having a changeable color and comprising at least one light emitting diode emitting primary radiation,
A layer connected to the light emitting diode, the layer comprising at least one luminescent material that converts the primary radiation into secondary radiation;
A switching device that drives the diode with a pulse-shaped current to supply light comprising the primary radiation and / or the secondary radiation, each independently changing the brightness and color of the light A switching device that adjusts the saturation of the luminescent material by the energy density per pulse and controls the overall light output by the number of pulses,
Having a light source.   The light source according to claim 1, wherein the pulse-shaped current is pulse-width modulated.   The light source according to claim 1, wherein the primary radiation is visible light or invisible light.   The light source according to claim 1, wherein the light emitting material is a phosphor. The layer is
(red)
CaS: Eu, SrS: Eu, (Ca, Sr) S: Eu, (Y, Gd) ₂ O ₂ S: Eu, Y (VO ₄ ): Eu, (Sr, Ba, Ca) ₂ Si ₅ N ₈ : Eu,
(Green / yellow)
_{Y 3 Al 5 O 12: Ce} , (Y, Gd) 3 A l5 O 12: Ce, (Ba, Sr, Ca) 2 SiO 4: Eu, CaS: Ce, ZnS: Cu, La (PO 4) :( _{Ce, Tb), (Ce,} Tb) Al 12 O 19, (Ce, Gd, Tb) MgB 5 O 10, BaMgAl 10 O 17: Eu, Mn, ZnS: Au,
(Blue)
CaS: Cu, SrS: Ag, ZnS: Ag, BaMgAl ₁₀ O ₁₇ : Eu or (Ca, Sr, Ba) ₅ (PO ₄ ) ₃ Cl: Sb, (Ca, Sr, Ba) ₅ (PO ₄ ) ₃ Cl : Eu,
(White)
(Ca, Sr, Ba) ₅ (PO ₄ ) ₃ (F, Cl): Sb, Mn, (Ca, Sr, Ba) ₅ (PO ₄ ) ₃ (F, Cl): Eu, Mn
5. The light source according to claim 1, comprising at least one or a combination of the phosphors. The light source according to claim 1, wherein the phosphor material of the layer has a density of 1.5 g / cm ³ ≦ d ≦ 10 g / cm ³ .   The light source according to claim 1, wherein the layer includes phosphor particles, and the layer includes at least one granular layer. The layer is characterized by having x number of granular layers is 1 ≦ x ≦ 10, light source according to claim 7. Use of a light source comprising at least one light emitting diode emitting primary radiation and having a layer connected to the light emitting diode and comprising at least one luminescent material that converts the primary radiation into secondary radiation And steps to
Using a switching device that drives the diode with a pulsed current including a pulse width (pulse period) and a distance between pulses (switching off period), wherein the saturation of the luminescent material is the energy per pulse. Adjusting the density and controlling the overall light output by the number of pulses;
A method of generating light having
The luminescent material having an attenuation period is excited by the primary radiation so as to change the brightness and color of light including the primary radiation and / or the secondary radiation exiting the light source independently of each other, and the pulse width Is equal to the decay period.   10. A method according to claim 9, characterized in that the distance between the pulses is greater than the decay period of the luminescent material, in particular the distance between the pulses is at least twice as large as the decay period.   The brightness of the light exiting the light source can be changed by changing the distance between the pulses, whereby the color of the light is substantially constant. Method.   12. A method according to any one of claims 9 to 11, characterized in that the color of the light can be changed by changing the intensity of the pulsed current.   The method according to any one of claims 9 to 12, wherein the light source according to any one of claims 1 to 8 is used.

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